AES3 Passive Converters

October 11, 2001

AES3 Passive Convertors

AES3 digital signals are being used more and more everyday. There
are two versions of this standard. One is a balanced signal passed over
a twisted-pair wire with a characteristic impedance of 110 ohms. Its
complete name is AES3-1992. The other is an unbalanced signal passed
over coaxial cable with a characteristic impedance of 75 ohms. This is
called AES3-ID-1995. Both formats are commonly referenced without the
last four digits, which indicate the year the standard was
adopted.

Apart from the voltage level and ground reference, the formats are
identical. The passive circuit below can be used to convert signals
from one format to the other. Both circuits account for the difference
in impedance. The balanced-to-unbalanced converter also reduced the
voltage level. Because these are passive circuits, the
unbalanced-to-balanced converter cannot increase the voltage level.
This circuit is better suited to applications where a long signal path
is needed and an amplifier can be placed at the receiving end.

A balanced signal must not only be unbalanced, but also reduced in
level by 14dB. The circuit below has a load impedance of 112 ohms, a
source impedance of 72 ohms, a return loss of >25dB, and an
atenuation of 1:5 (14dB).